Require explicit use of `use_frameworks!`

Closes #3029

[ExternalSource] Coerce podspec string contents to json to store in the ...

Closes https://github.com/CocoaPods/CocoaPods/issues/2685.

[RuboCop] Favor if over unless for negative conditions. Don't use parentheses around the condition of an if.

Closes https://github.com/CocoaPods/CocoaPods/issues/2992.

implemented Xcode license check for `pod setup`

Copy Swift libraries using `rsync -u`

This should ensure that they're not recopied if unchanged, because the
destination will be newer if they changed due to code-signing.

[Installer] Reject installation if a static library is used as a transit...

[Installer] Reject installation if a static library is used as a transitive dependency while integrating Pods as frameworks.

Configure as extension only for watch extensions

[Frameworks] Fail lint for Swift on iOS < 8.

Since we now have our own error for this, it should be filtered,
especially considering that it might be confusing for people linting
with `--use-frameworks`.

Have to use dynamic frameworks for Swift and they are unsupported on iOS
7.

Closes https://github.com/CocoaPods/CocoaPods/issues/3158.

Closes #3134